The present invention relates to a transesterification method with a powdery lipase.
The transesterification reaction is an important means for the reforming of animal and vegetable oils and fats and also for the production of various fatty acid esters, saccharide esters and steroids. When a lipase which is an enzyme for hydrolyzing oils and fats is used as the catalyst for the transesterification reaction, the following merits are obtained: this reaction can be conducted under mild conditions of room temperature to about 70.degree. C.; the side reactions can be controlled and the energy cost can be lowered more easily than in ordinary chemical reactions; and a high safety is attained, since the lipase used as the catalyst is a natural product. Another merit is that the intended product can be efficiently produced, based on the substrate specificity and site specificity.
However, when the powdery lipase is used as it is for the transesterification reaction, its activity cannot be sufficiently exhibited. Moreover, it is difficult to homogeneously disperse the essentially water-soluble lipase in the oily starting materials and, in addition, the recovery thereof is also difficult. Therefore, the lipase is usually immobilized on a carrier such as an anion-exchange resin [Japanese Patent Unexamined Published Application (hereinafter referred to as "J.P. KOKAI") No. Sho 60-98984), phenol adsorbent resin (J.P. KOKAI No. Sho 61-202688), hydrophobic carrier (J.P. KOKAI No. Hei 2-138986), cation-exchange resin (J.P. KOKAI No. Hei 3-61485) or chelate resin (J.P. KOKAI No. Hei 1-262795) in order to use it for the transesterification reactions of the oils and fats.
Although the lipase to be used for the transesterification reaction was immobilized in the prior art, the immobilization causes a loss of the essential activity of the lipase and, in addition, when a porous carrier is used, the pores are clogged with the starting materials and the product to lower the transesterification efficiency. Further, in the transesterification reaction with the conventional immobilized lipase, water contained in the carrier is introduced into the reaction system and, therefore, it is difficult to avoid side reactions such as the formation of a diglyceride or monoglyceride in the course of the transesterification reaction of the oils and fats.
It has been scarcely known in the field of the transesterification reaction with the ordinary lipase that a lipase is usable at a reaction temperature of as high as around 100.degree. C. whether the lipase is immobilized or not. The reasons therefor are supposedly that no lipase resistant to such a high temperature has been found yet and that such a heat-resistant, immobilized lipase was not developed in the conventional immobilization technique.